1. Field of the Invention
The present invention relates to a sample treatment apparatus for treating coexistent components adhering to a sample flow channel and a measuring apparatus for providing it.
2. Description of the Related Art
In a process of producing various petroleum products from heavy oil as raw material, a gas containing a large amount of hydrogen sulfide (H2S) discharged from a refining apparatus, a catalytic cracking apparatus or the like, generates sulfur dioxide (SO2) significantly when the discharged gas is used directly as fuel gas, so conventionally the gas is used after sulfur contained therein is removed by a sulfur recovery apparatus. Specifically, the recovery of sulfur comprises a step of separating H2S from the gas and a step of converting the separated H2S into element sulfur (Sv). The former step uses a method that involves absorbing H2S into an aqueous alkaline solution of monoethanolamine etc. and then separating and recovering it, and the latter step widely uses the Claus process or Super Claus process.
As the most important and effective sulfur recovery process, the Claus process or Super Claus process is used in gas treatment, in natural gas and cokes plants and in a refining apparatus. In this process, a part of the acidic gas stream is oxidized to generate SO2. Thereafter, SO2 reacts with remaining H2S to form sulfur in the presence of a catalyst. Due to easiness and efficiency, the Claus process is useful in recovery of sulfur and utilized more often worldwide than in any other plants.
The Claus process is a process wherein H2S is converted into Sv by the following chemical reactions:    (1) H2S is partially combusted with air in a reaction furnace and partially formed into SO2.3H2S+3/202=2H2S+SO2+H2O  (1)    (2) Then, this gas is introduced into a catalytic reaction tower (catalytic reaction means) to form gaseous Sv.2H2S+SO2=3Sv+2H2O  (2)
By the Claus process shown above, the recovery of sulfur is sometimes known to be as high as 98% or more.
Throughout the stoichiometric reactions in the catalytic reaction tower, the critical ratio in the Claus process should be kept at 2:1 to obtain Sv surely in a good yield. This is evidence from the fact that when the ratio is 2:1 or more, excessive oxygen (O2) is necessary in the process. Because air is used in combustion in the reaction furnace, the oxygen demand in the reaction shall usually be the air demanded for the reaction.
As the method of removing and recovering Sv from the gas stream in the Claus process described above, there is proposed a method that involves cooling the gas to be processed, whereby Sv in the form of steam and/or entraining particles is removed from the gas. Specifically as shown in FIG. 5, the gas to be processed is led toward the lower end of a heat exchanger 104, and it is guaranteed by the temperature and/or the flow rate of a refrigerant that the temperature of a wall surface of the heat exchanger 104 is not higher than the solidification point of sulfur, or is not lower than the dew point of water if any in the gas. By the action of gravity, the precipitated Sv is removed toward the direction opposite to the flow of the gas to be processed (see, for example, JP-A 8-224438).
In the Claus plant or the like, however, the recovery of sulfur is influenced significantly by the concentration of H2S and SO2 involved in the reaction, and thus it is important to measure the concentration of H2S and SO2. That is, accurate measurement of H2S and SO2 is key to optimization of the sulfur recovery process. Examples of the measurement method include a method of using ultraviolet (UV) absorption spectrometry capable of separate and direct measurement of H2S and SO2 or a method that involves oxidizing a reducing sulfur compound such as H2S into SO2 to measure the concentration of H2S indirectly by infrared (IR) absorption spectrometry thereby determining the concentration of H2S and SO2.
Because of Sv and water present in the process gas, the measurement may undergo the interference influence attributable to overlapping of absorption spectra of H2S and SO2 or influence attributable to splashing, clogging resulting or the like from aggregation. Particularly in measurement of a sample collected in a process and in measurement by a directly inserted measuring apparatus, the operation of the measuring apparatus in a suitable state for 4 to 8 months is necessary, and thus such influence cannot be neglected.
In the former measuring apparatus of sample collection type, an apparatus for removing Sv is necessary in an absorbance measuring unit in measuring H2S and SO2, in order to eliminate the interference influence caused for example by highly UV absorption characteristics of Sv. Further, crystallization and clogging with Sv occur easily, thus making it necessary to remove easily solidified substances such as Sv in a sample treating part in the measuring apparatus of sample collection type.
In the directly inserted measuring apparatus, a cold trapping system is used sometimes to eliminate the contamination of a measuring flow cell with sulfur, but crystallized sulfur is layered to form a thermally insulating layer, resulting in failure to maintain a suitable cooling function. Elimination of such excessive sulfur is problematic.
It is generally difficult to continuously measure a gas containing not only the above-mentioned Sv but also a gas containing crystallizing or condensing/solidifying substances (for example, tar in coal liquefied gas), and at present, a gas is collected in, for example, a Tedrer® bag and analyzed batch-wise.
When a means (e.g. a feed pump) of exerting an influence on the pressure or temperature of a sample is arranged in a sample collection system to measure such a gas, the change in the pressure or temperature may induce generation of condensates thereby.